A big drop of ingenuity

Rainwater harvesting is the perfect answer to the new standards for water consumption in sustainable homes, says Steff Wright, chairman of the Gusto Group and a member of the Rainwater Harvesting Association

In Part-G of the updated Building Regulations, which took effect on 6 April, a number of revolutionary changes of approach become evident, in particular, the inclusion of a new emphasis on the environmental performance resulting from the regulations, to sit alongside their traditional health and safety role. As far as water is concerned, Requirement G-1 of the updated regulations introduces the opportunity to consider use of two standards of water in a dwelling, namely ‘wholesome’ water for drinking, bathing, cooking and dish-washing, and ‘non-wholesome’ water of a suitable quality for uses such as toilet flushing, clothes washing and the outside tap.

Associated Guidance Notes go on to describe a number of potential sources of non-wholesome water, harvested rainwater being the most commonly available and straightforward. Requirement G-2 of the updated regulations go on to make clear why this distinction suddenly becomes important to the house-building industry, by stipulating that the potential consumption of wholesome water by persons occupying a dwelling must not exceed 125l/day per person. This compares with the current national average assumed by the Code for Sustainable Homes (150l/day), and equates to the water consumption requirements of Levels 1 and 2 of the Code.

This Regulation applies to all new dwellings, but the Government has already imposed higher requirements on houses being built with public money, namely water consumption of no more than 105l/day. By 2016, the policy intention is that all new homes will be built to Code Level 5 or 6, reducing the demand on mains water still further to 80l/day per person.

Of particular interest to the house-building industry will be the refusal of authorities to sign-off completion of a property until its water-related performance has been demonstrated. This must be done by providing all necessary data, such as the manufacturer’s specifications for water-related fixtures and fittings, in the format required by the Government’s Water Efficiency Calculator for New Dwellings. A ‘credit’ is given within the calculator for any wholesome water usage displaced by using nonwholesome water where appropriate.

Rainwater harvesting (RWH) systems are particularly relevant in this respect, as they are capable of meeting most of a household’s toilet-flushing, clothes washing and outside tap requirements which account for around half of all domestic water consumption. This is reflected in independent Environment Agency monitoring of systems installed at Gusto Homes’ flagship Millennium Green development, completed in 2002. This showed that in a selected home, harvested rainwater provided around 50% of all the water used.

Very broadly, a property with a 100m2 roof in an area with typical UK rainfall, say 650mm per annum, would provide nearly all the water needed for non-wholesome applications, thus reducing wholesome water consumption by up to 50%. This would be particularly helpful in meeting the higher levels of the Code for Sustainable Homes, and is similarly applicable for the BREAAM ratings on commercial developments where the savings can exceed 80%.

This emphasis on water consumption reflects the stress on national water supplies, particularly in the more highly populated regions of England South of the Humber estuary. These stresses are likely to intensify with the growth in national population, predicted by the Environment Agency to increase by 20M over the next 40 years. Harvesting rainwater is a well-tried response to meeting local water needs, albeit one that largely died out in the UK with the availability of a mains system delivering safe drinking water direct to the tap. Now the wheel is turning full circle with the need to supplement national mains water supplies with more traditional approaches.

Modern RWH systems are entirely automatic and, from the users perspective, indistinguishable in use from using mains water for the same application. They simply channel the water falling onto the roof via a filter to a storage tank, from where it is pumped on-demand to either direct to the appliance concerned or via a header-tank. To ensure continuity of supply during prolonged dry periods the system arranges for the storage or header tank to be topped-up from the mains supply via an air-gap, whilst during prolonged wet spells the storage tank overflows into the surface water management arrangements for project. RWH systems are the perfect answer to the new requirements set out in the updated Part-G of the Building Regulations, helping to meet mains water consumption requirements, assisting with the surface water management arrangements for the site, and playing a part alleviating down-stream flood risks.

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